A study claiming that marijuana has negative effects on the brains of casual users made waves earlier this month. But at least one scientist claims the research misrepresents the truth.
"The paper is terrible on a number of levels," Lior Pachter, a computational biologist and professor at the University of California, Berkeley, told The Huffington Post. "It reeks of dishonesty."
Pachter, who says he doesn't smoke pot or use any other drugs, has blogged about what he sees as flaws in the study. He told HuffPost that after closely examining the research, he came to the conclusion that not only did the scientists involved use flawed methodology, they then misrepresented their findings to the media.
Published by The Journal of Neuroscience, the study takes a look at three aspects of the brain morphology of 20 marijuana users aged 18-25. The researchers examined the density, volume and shape of the marijuana users' gray matter, and compared their brains to those of 20 non-marijuana users. The report concluded that two areas of the brain associated with emotion and motivation -- the amygdala and the nucleus accumbens -- were shaped differently and had a higher density in the marijuana users' brains.
On his blog, Pachter suggests that the researchers cherry-picked their data to arrive at the conclusion they were looking for, and questions the statistical significance of the results they generated.
Pachter also argues that the report merely shows correlation, not causality. At minimum, he says, the researchers would have had to do a study of marijuana users over a longer period of time in order to reach the conclusion the researchers state in the abstract.
"Given what they did, the best they could hope to say was that they found a correlation between pot use and some aspect of the brain," Pachter said. "The problem is that this is very different from causation. Maybe users have strange brains because they smoked pot. But maybe they smoke pot because they have strange brains. There is an important difference here."
Pachter also took issue with the way one of the researchers presented the data to the media. In a press statement regarding the report, Dr. Hans Breiter, a professor of psychiatry and behavioral sciences at Northwestern University's Feinberg School of Medicine and a co-author of the study, said:
"Some of these people only used marijuana to get high once or twice a week. People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school. Our data directly says this is not the case."
On his blog, Pachter criticized Dr. Breiter's statement, calling it a "lie" and alleging that the description does not reflect the findings of the report accurately.
"The repeated use of words like 'recreational' and 'casual' suggest they are talking about people occasionally using some pot," Pachter told HuffPost. "In reality, their average user was doing more than 11 joints a week. I don't know that much about pot but that seems to be a lot. Again, it seems dishonest."
Breiter defended his and his colleagues' research to HuffPost, maintaining that their sample size was not too small for the design and purpose of the study, that the reported findings are in no way misleading and that the results of their findings are unambiguous. He did add that future longitudinal studies are needed to fully flesh out the findings.
"Dr. Pachter's allegations are false and misleading," Breiter said. "He is clearly unfamiliar with the field of neuroimaging and its conventions. We are confident in the quality of our work, the stringent peer review process at The Journal of Neuroscience, and our own integrity. We know Dr. Pachter's criticisms do not apply."
But other experts agree with Pachter's assessment. Dr. Asaf Keller, a professor of anatomy and neurobiology at the University of Maryland School of Medicine who has done research related to the effects of marijuana use on the teen brain, told HuffPost that the study "suffers from several shortcomings in design, statistical analysis and -- most importantly -- in interpretation."
"The hype surrounding this manuscript is unwarranted," Keller said. "The sample size is woefully small. The statistical methods used -- to the extent that they can be assessed from the very brief descriptions in the manuscript -- are inappropriate. Even if the study was done appropriately, the results do not reach statistical significance."
Dr. Susan Tapert, a neuroscientist at the University of California, San Diego, who has also done research on marijuana's effects on teen brain tissue, told HuffPost that she didn't think the research was flawed. However, she added, she believed it was "limited in how much it can tell us" due to its sample size and scope.
"The study does spur interest on the topic," she said. "Given how widespread marijuana now is, we certainly should invest in long-term studies that follow people over time to see how starting, increasing and stopping marijuana use changes the brain and cognition."
John Maunsell, editor-in-chief of The Journal of Neuroscience, told HuffPost that the editorial board does not comment on specific articles.
Pachter, for his part, went so far as to suggest that Breiter should be sanctioned for misleading the media about his work.
"Lots and lots of people care deeply about the issue, and major policy decisions will have to be made using the type of information in the study," he said. "The nature of the paper, coupled with the statements made by the last author in the press releases, made me very, very angry, because the actions will hurt a large number of people."